The present invention relates to a method for coating a tip region of a multipolar electrode head, of the type adapted to be mounted at a distal end of an electrode lead (pacing lead) used preferably for providing intracardial stimulation of heart tissue, and/or for sensing heart signals, by means of a heart stimulation apparatus or pulse generator.
A heart stimulation apparatus having an electrode device with a multipolar electrode head is disclosed in U.S. Pat. No. 5,306,292. This electrode head is a hemispherical electrode head fitted with a number (e.g. four) of round, closely spaced conductive surfaces that are uniformly distributed on the electrode head. The conductive surfaces are separated y an electrically insulating material, normally a ceramic material such as aluminum. The conductive surfaces are normally coated with a porous layer, such as titanium nitride (TiN) intended to enlarge the active surface of each conductive surface. At present the belief is that the conductive surfaces should be coated utilizing masking operations to avoid the coating material being deposited on the insulating material, to ensure that each conductive surface is in electrical contact only with tissue/body liquid and the conductor in the lead.
An object of the present invention is to devise a simplified method of manufacturing multipolar electrode heads with a porous layer.
The above object is achieved in accordance with the present invention in a method for coating a tip region of a multipolar electrode head, adapted to be mounted at a distal end of a lead preferably used for providing heart stimulation by connection to a heart stimulation apparatus, wherein an electrode head is provided having a tip with a ceramic part in which a number of small, spaced-apart conductive electrode surfaces are disposed, and wherein a region of the electrode head tip is directly coated with a tissue compatible material, so that all conductive electrode surfaces are coated in a single step coating operation without any masking operation.
The method consequently excludes the masking operation hitherto thought necessary. To be able to dispense with a masking operation greatly simplifies the manufacture of this type of electrode.
The invention is based on the surprising insight that it is possible to allow the porous layer to extend wholly or partly over the insulating material between the conducting surfaces, the dimensions, i.e. the effective conductive cross-section, of the porous layer being such that the electrical conduction through the tissue/body fluid between the conductive surfaces is not affected, this being due to the thinness of the layer as well as being due to the porosity of the material in the layer.
As a suitable coating material is preferably a porous material, the resistivity of which is at least equal to, but preferably higher than, the resistivity of cardiac body fluids. The thinness and porosity, i.e. the effective conductive cross-section, of the layers as well as the distance between the electrode surfaces are taken into account for determining the resistivity. Materials suitable for the coating step are preferably titanium nitride, carbon and platinum black.
The above object is also achieved in accordance with the principles of the present invention in a method for manufacturing a multipolar electrode head by providing a non-conductive part, such as a ceramic part, with a number of recesses or notches therein, inserting respective conductive wires into the recesses or notches to form a number of spaced-apart electrodes, separated by the non-conductive material, and directly coating the surface of the non-conductive material, with the electrodes formed therein, so as to coat all of the electrodes in a single coating step, without the use of a masking operation.